Spontaneously occurring mother–infant swapping and the relationships of infants with their biological and foster mothers in a captive group of lowland gorillas (Gorilla gorilla gorilla)

The present study describes spontaneously occurring infant–mother swapping and the relationships of infants with their biological and foster mothers after swapping in a captive social group of lowland gorillas (Gorilla gorilla gorilla). After infant-swapping took place between a primiparous mother with a neonate and a multiparous mother with a 10-month-old infant, the mothers provided appropriate maternal care, including nursing, to their adopted infants, but the older infant still sought refuge with its biological mother more frequently than with its foster mother. Almost 2 years later, the younger infant who was weaned by its foster mother began nursing from its biological mother; the latter subsequently weaned her adopted infant. Thereafter, the older infant who was weaned exhibited an abnormal hair-plucking behavior. These results indicate that it was psychologically stressful for the gorilla infant to quickly transfer its attachment figure from the mother to another adult female when the mother continued to remain in the group.